Stabilising and functional effects of Spirulina (Arthrospira platensis) protein isolate on encapsulated Lacticaseibacillus rhamnosus GG during processing, storage and gastrointestinal digestion

The present study investigated Spirulina (Arthrospira platensis) protein isolate (SPI) for its ability to preserve the biological activity of L. rhamnosus GG (LGG) cells under diverse physicochemical stressors associated with the lyophilisation process, storage, and in vitro digestion. The lyoprotective and stabilising effects of SPI were compared to whey protein isolate (WPI) and pea protein isolate (PPI). The microstructural, physicochemical, and thermal properties of the probiotic lyophilisates were also assessed. Overall, SPI demonstrated superior lyoprotective and storage stabilising effects compared to WPI, although it was less efficient than PPI. Elevated storage temperature and relative humidity (RH) conditions accelerated LGG inactivation rates, especially in the case of WPI, which was primarily attributed to increased LGG's metabolic activity. The fermentation of the probiotic freeze-drying media impaired LGG's ability to withstand the physicochemical stressors during lyophilization and storage. However, the pre-fermentation step improved LGG's resistance to harsh acidic conditions in simulated gastric fluids. Bile salts and pancreases did not significantly affect LGG's survivability, with WPI and PPI showing the most effectiveness. Employing an in vitro co-culture model of the gut epithelium, WPI and PPI demonstrated satisfactory adhesion of LGG cells to the mucus layer, displaying the highest cell adhesion potential. In conclusion, SPI appears to be a promising wall material for probiotic cell encapsulation, serving as an alternative to WPI.